The present invention provides for an improved process for separating and removing nitrogen oxides, sulfur oxides, heavy metals and other contaminants from exhaust gases. These exhaust gases include those that originate from any full or partial combustion source, thermal processes, and process off gases from fossil fuel fired boilers, furnaces, incineration plants, refining, petroleum and petrochemical plants, inorganic, organic, fine and bulk chemical production plants.
Recent federal and local environmental laws require very significant reduction of discharge of harmful gaseous substances into the atmosphere. Chief among such harmful air pollutants are nitrogen oxides (NOx). In response to strict enforcement efforts of these laws, industrial air polluters have made considerable efforts to reduce the amount of these harmful substances into the air in gaseous effluents from industrial or municipal sources. Successful efforts to reduce the concentration of NOx in gaseous effluents often involve reacting the NOx in waste gases with nitrogen-based reducing agents.
Another known method of removing NOx from gas streams involves contacting the NOx with ozone, thereby oxidizing them to higher nitrogen oxides, such as N2O5 and removing the higher oxides from the gas stream by means of aqueous scrubbers.
Specific details of ozone-based NOx oxidation processes are disclosed in U.S. Pat. Nos. 5,206,002; 5,316,737; 5,985,223; and 6,197,268, the disclosures of which are incorporated herein by reference.
Additionally, the Environmental Protection Agency has presented information showing mercury levels in the environment are at levels that are likely to lead to adverse health effects. Coal-fired utility boilers are one of the largest sources of harmful anthropogenic mercury emissions but also include the NOx and SOx emissions sources. The present inventors have discovered a process whereby heavy metals as well as NOx and SOx can be removed from the emission from a variety of industrial processes.